Summary

Many protein functions can be attributed to segments (domains) that fold independently and adopt specific three-dimensional structures (1). Intrinsically disordered regions (2, 3) are unstructured segments whose amino acid compositions prevent autonomous folding. Some eukaryotic proteins are either fully disordered (intrinsically disordered proteins) or structured, but most have both types of regions (see the figure). The notion that disordered regions are largely passive is being actively challenged by the idea that they perform diverse functions, and that synergy between structured and disordered regions expands the functional repertoires of proteins.